Control for a two stage master cylinder

A two stage master cylinder comprising:

• a housing having a first diameter bore separated from a larger second diameter bore by a shoulder and a reservoir connected to said first diameter bore;
• a first piston located in said first diameter bore and cooperating with said housing to define a first chamber in said first diameter bore;
• a second piston having a first cylindrical body with a first diameter section extending from a second diameter section into said first diameter bore and cooperating with said housing and said first piston to define a second chamber in said first diameter bore, said second diameter section cooperating with said first diameter section, said shoulder, and said housing to define an actuator chamber in said second diameter bore, said first cylindrical body having a stepped axial bore extending through said first diameter section to a point adjacent said second diameter section, said first cylindrical body having a first radial passage for connecting said actuation chamber with said axial bore and a second axial passage for connecting said axial bore to said reservoir;
• shuttle means located in said stepped axial bore of said first cylindrical body having a first surface exposed to the fluid in said second chamber and a second surface exposed to the fluid in said actuation chamber, said first surface being larger than said second surface;
• first seal means associated with said shuttle means for controlling the communication of fluid from said stepped axial bore into said second chamber and said reservoir;
• resilient means connected to said shuttle means for urging said first surface toward said second chamber;
• and
• input means connected to said second piston and responsive to an input force for moving said first diameter section in said first diameter bore and said second diameter section in said second diameter bore to create an actuation fluid pressure in said actuation chamber and an operational fluid pressure in said second chamber, said actuation fluid pressure being communicated to said second chamber by flowing through said first radial passage into said stepped axial bore and around said first seal means, said operational fluid pressure acting on said first surface and moving said shuttle means in opposition to said resilient means and actuation fluid pressure acting on said second surface to communicate said axial bore to said reservoir and thereby relieve the actuation fluid pressure from said second bore to permit the entire input force to be communicated into said second piston means for moving said first diameter section in the first diameter bore and pressurize the fluid in the second chamber;
• a first groove on said second piston located between a first land and a second land on the first diameter section of said first cylindrical body, said second radial passage terminating in said first groove adjacent said first land, said first groove connecting said second radial passage with said reservoir upon movement of said second piston;
• a second groove on said second piston located on said first diameter section, said second groove being connected to said first groove to permit fluid communication between said actuation chamber and the reservoir upon termination of the operator input force;
• second seal means located adjacent said shoulder on the housing having a lip which projects into said second groove, said lip engaging said first diameter section of said first cylindrical body to prevent communication of fluid from the actuation chamber upon movement of said second piston means;
• and
• said shuttle means including a second cylindrical body having a first section separated from a second section by a second shoulder, said second shoulder cooperating with said stepped axial bore and the first section of said second cylindrical body to define a dampening chamber, said dampening chamber being connected to said first groove by a third radial passage in said first cylindrical body, said third radial passage metering fluid to said first groove to control the rate of movement of said shuttle means.